Recording/reproducing apparatus and recording/reproducing system

ABSTRACT

A recording/reproducing apparatus includes an optical source and a near-field light generating unit. The near-field light generating unit includes two conductors facing to each other at a predetermined distance and generating near-field light between the two conductors by irradiation of light from the optical source. These two conductors are arranged so that a direction along which the two conductors face to each other is substantially in parallel with the longitudinal direction of a recording mark region. Here, the recording mark region is prepared from a predetermined recording material and having shape anisotropy when information is recorded on a recording medium on which the recording mark is independently formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording/reproducing apparatus and arecording/reproducing system. More specifically, the present inventionrelates to a recording/reproducing apparatus and a recording/reproducingsystem, which use near-field light.

2. Description of the Related Art

In recent years, various technologies using near-field light asrecording light have been proposed to realize higher recording densityon an information recording medium (see, for example, Japanese PublishedPatent Application Nos. 2005-202987 and 2003-308632). The use ofnear-field light realizes a minute light spot beyond a diffraction limitof light can be realized. Therefore, for example, attentions have beenpaid on a heat-assisting magnetic recording technology using near-fieldlight as a promising technology for high density magnetic recording. Inaddition, various applications of near-field light to an informationrecording medium using a magneto-optical recording film and aphase-change recording film have been proposed.

A recording/reproducing apparatus proposed in Japanese Published PatentApplication No. 2005-202987 performs information recording on recordinglayers (recording mark regions) each having a fine structure not largerthan the wavelength of incident light by irradiation of near-field lightfrom a minute opening of a probe where the diameter of the opening isnot larger than the wavelength of the incident light. In JapanesePublished Patent Application No. 2005-202987, furthermore, an opticalinformation recording medium includes recording layers (recording markregions) with circular fine structures formed independently from oneanother when viewed from the light-irradiation side.

A recording/reproducing apparatus proposed in Japanese Published PatentApplication No. 2003-308632 performs information recording on recordinglayers formed on fine structure layers not larger than the wavelength ofincident light by irradiation of near-field light from a minute openingof a probe where the diameter of the opening is not larger than thewavelength of the incident light.

As a method of generating near-field light other than one using a probeas described in the above patent documents, for example, there is amethod using surface plasmon resonance generated on the surface of aconductor when light is irradiated on the conductor. In this method, forexample, if the polarization direction of light is aligned with thelongitudinal direction of a rectangular conductor formed on atransparent substrate when light is irradiated on the conductor,electric charges are localized in the conductor under the electric fieldof incident light. Oscillation generated by localization of the chargesis known as surface plasmons. When a resonance wavelength of surfaceplasmons is equal to a wavelength of incident light, surface plasmonsare brought into a resonance state called surface plasmon resonance. Inthis case, the conductor becomes an electric dipole, which is stronglypolarized in the longitudinal direction of the conductor. When theconductor becomes the electric dipole, a large electromagnetic field isgenerated near the both ends in the longitudinal direction of theconductor to generate near-field light.

SUMMARY OF THE INVENTION

In the optical information recording medium described in the aboveJapanese Published Patent Application No. 2005-202987 and a magneticrecording medium called a patterned medium used for a hard disk or thelike, recording mark regions (hereinafter, also simply referred to as arecording marks) are formed independently. In general, the recordingmark has an isotropic shape (for example, a circular shape) when viewedfrom the light-irradiation side. If near-field light is irradiated onsuch a recording mark having an isotropic shape, there is no change inamount of light absorbed in the recording mark in principle even whenthe positional relationship between the recording mark and a structuralcomponent generating near-field light (such as conductor) is changed.

However, if the recording mark formed on the patterned medium or thelike has shape anisotropy when viewed from the light incident side, achange in amount of light absorbed in the recording mark may occurdepending on the positional relationship between the recording mark andthe structural component generating the near-field light. In this case,the near-field light may not be efficiently absorbed depending on theirpositional relationship.

In consideration of the aforementioned circumstance, it is desirable toprovide a recording/reproducing apparatus and a recording/reproducingsystem, which allow recording marks with shape anisotropy independentlyformed on a recording medium to efficiently absorb near-field light.

A first embodiment of the present invention is a recording/reproducingapparatus that includes an optical source and a near-field lightgenerating unit generating near-field light between two conductorsfacing to each other with a given distance by irradiation of light fromthe optical source. In such a recording/reproducing apparatus, these twoconductors are arranged so that a direction along which the above twoconductors face to each other is substantially in parallel with thelongitudinal direction of the recording mark region prepared from apredetermined recording material and having shape anisotropy wheninformation is recorded on a recording medium on which the recordingmarks are independently formed.

The term “substantially in parallel with” or “substantially parallel to”used herein means that the direction along which the two conductors faceto each other and the longitudinal direction of the recording markregion may be completely parallel to each other or may be slightlydeviated from such a completely parallel state because of productiontolerance.

A second embodiment of the present invention is a record reproductionsystem that includes a recording medium, an optical source, and anear-field light generating unit. Here, on the recording medium,recording mark regions having shape anisotropy are independently formedof a predetermined recording material. Also, the near-field lightgenerating unit includes two conductors facing to each other at apredetermined distance and generating near-field light between these twoconductors by irradiation of light from the optical source. In addition,these two conductors are arranged so that a direction along which theabove two conductors face to each other is substantially in parallelwith the longitudinal direction of the recording mark when informationis recorded on a recording medium using the near-field light.

According to any of embodiments of the present invention, two conductorsare arranged so that a direction along which two conductors face to eachother is substantially in parallel with the longitudinal direction ofthe recording mark when near-field light is used for recordinginformation on a recording medium on which recording marks having shapeanisotropy are independently formed. Therefore, the near-field light canbe efficiently absorbed in the recording marks having shape anisotropy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the configuration of arecording/reproducing apparatus according to a first embodiment of thepresent invention;

FIG. 2 is a schematic diagram of near-field light generating unit of thefirst embodiment, where FIG. 2A is a top view of the near-field lightgenerating unit and FIG. 2B is a cross-sectional view along the dashedline IIB-IIB in FIG. 2A;

FIG. 3 is a diagram illustrating the analytical conditions of asimulation analysis employed in the first embodiment;

FIG. 4 is a diagram illustrating the results of analyzing thefield-intensity distribution of near-field light in the firstembodiment, where FIG. 4A is a graphical representation of the fieldintensity in the X direction and FIG. 4B is a graphical representationof the field intensity in the Y direction;

FIG. 5 is a schematic diagram illustrating the configuration of arecording/reproducing system according to the first embodiment of thepresent invention;

FIG. 6 is a schematic diagram illustrating a state around the boundarybetween a flying slider head and a recording medium during aninformation-recording process;

FIG. 7 is a schematic diagram illustrating a positional relationshipbetween two conductors and recording marks;

FIG. 8 is a schematic diagram illustrating the configuration of a pairof conductors in a first modified example;

FIG. 9 is a schematic diagram illustrating analytical conditions of asimulation analysis in the first modified example;

FIG. 10 is a diagram illustrating the results of analyzing thefield-intensity distribution of near-field light in the first modifiedexample, where FIG. 10A is a graphical representation of the fieldintensity in the X direction and FIG. 10B is a graphical representationof the field intensity in the Y direction;

FIG. 11 is a schematic diagram illustrating the configuration of a pairof conductors in a second modified example;

FIG. 12 is a schematic diagram illustrating analytical conditions of asimulation analysis in the first modified example;

FIG. 13 is a diagram illustrating the results of analyzing thefield-intensity distribution of near-field light in the second modifiedexample, where FIG. 13A is a graphical representation of the fieldintensity in the X direction and FIG. 13B is a graphical representationof the field intensity in the Y direction;

FIG. 14 is a schematic diagram illustrating the configuration of a pairof conductors according to a third modified example of the presentinvention;

FIG. 15 is a schematic diagram illustrating analytical conditions of asimulation analysis in the third modified example;

FIG. 16 is a diagram illustrating the results of analyzing thefield-intensity distribution of near-field light in the third modifiedexample, where FIG. 16A is a graphical representation of the fieldintensity in the X direction and FIG. 16B is a graphical representationof the field intensity in the Y direction;

FIG. 17 is a schematic diagram illustrating analytical conditions when achange in optical absorption efficiency of a recording mark at the timeof changing the shape of the recording mark and the polarizationdirection of light are investigated by a simulation analysis;

FIG. 18 is a characteristics chart illustrating changes in amount ofrise in temperature of a recording mark when the shape of the recordingmark and the polarization direction of light are changed;

FIG. 19 is a schematic diagram illustrating analytical conditions when achange in optical absorption efficiency of a recording mark at the timeof changing the shape of the recording mark and the main field directionof near-field light are investigated by a simulation analysis;

FIG. 20 is a schematic diagram illustrating the configuration of arecording mark formed on a recording medium according to a fourthmodified example of the present invention;

FIG. 21 is a schematic diagram illustrating the configuration of arecording mark formed on a recording medium according to a fifthmodified example of the present invention;

FIG. 22 is a schematic diagram illustrating the configuration of arecording/reproducing system according to the sixth embodiment of thepresent invention;

FIG. 23 is a schematic diagram illustrating the configuration of arecording/reproducing head according to the sixth embodiment of thepresent invention;

FIG. 24 is a schematic diagram illustrating the configuration of arecording/reproducing apparatus according to a second embodiment of thepresent invention, where FIG. 24A is a schematic diagram illustratingthe configuration of a recording/reproducing system of the secondembodiment, and FIG. 24B is an enlarged cross-sectional view of a regionB surrounded by a dashed line in FIG. 24A;

FIG. 25 is a schematic diagram illustrating an optimal relationshipbetween the size of a gap between two conductors and a distance betweenthe conductor and a recording mark;

FIG. 26 is a schematic diagram illustrating an optimal relationshipbetween the size of a gap between two conductors and a distance betweenthe conductor and a recording mark;

FIG. 27 is a schematic diagram illustrating a relationship between afield intensity at Z=7 nm and a gap size g between two conductors;

FIG. 28 is a schematic diagram illustrating a relationship between afield intensity at Z=7 nm and a gap size g between two conductors;

FIG. 29 is a diagram illustrating the analytical conditions of asimulation analysis employed in the second embodiment; and

FIG. 30 is a diagram illustrating the results of a simulation analysisemployed in the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, exemplary configurations of recoding/reproducing apparatusand recording/reproducing system according to embodiments of the presentinvention will be respectively described with reference to the attacheddrawings. Their descriptions will be in the order of:

1. First embodiment: Example of basic configuration

2. Second embodiment: Example of configuration in which distance betweenrecording medium and near-field light generating unit is optimized

This invention is not limited to any of the following examples andembodiments.

1. First Embodiment Configuration of Recording/Reproducing Apparatus

FIG. 1 is a diagram schematically illustrating a section where anoptical near-field is generated (hereinafter, referred to as anear-field light production section) in a recording/reproducingapparatus according to a first embodiment of the present invention. Therecording/reproducing apparatus of this embodiment is an apparatus of anoptical recording system using near-field light or an apparatus of aheat-assisting magnetic recording system. The near-field lightproduction section 10 mainly includes an optical source 1, a collimatorlens 2, a condenser lens 3, and a near-field light generating unit 4.

The optical source 1 emits light (hereinafter, a propagating light) tothe near-field light generating unit 4. In this embodiment, thepropagating light Lp may be circularly-polarized light or may be lightlinearly polarized in substantially the same direction as the directionalong which two conductors 6 in pairs are facing to each other(direction “X” in FIG. 1).

In addition, the wavelength of propagating light Lp emitted from theoptical source 1 may be any wavelength as far as it allows thegeneration of near-field light between paired conductors 6 which will bedescribed later. For example, the propagating light used may be of 780nm in wavelength.

The collimator lens 2 makes the propagating light emitted from the lightsource 1 into collimated light. The condenser lens 3 condenses thecollimated light so that the propagating light Lp of a predeterminedspot size S can be irradiated on the near-field light generating unit 4.

The schematic configuration of the near-field light generating unit 4 isillustrated in FIG. 2. FIG. 2A is a top view of the near-field lightgenerating unit 4 and FIG. 2B is a cross-sectional view along a dashedline IIB-IIB in FIG. 2A. The near-field light generating unit 4 includesa substrate 5 and two conductors 6 formed on one side (the top) of thesubstrate 5. The propagating light Lp from the optical source 1 entersfrom the opposite side (the back) of the substrate 5, on which thepaired conductors 6 are not formed.

The substrate 5 is formed of a plate-shaped, optically transparentmember. In other words, the substrate 5 is made of a material which isoptically transparent at usable light wavelengths. For example, thematerial for forming the substrate 5 may be preferably one with atransmittance of approximately 70% or more. More specifically, any of IVgroup semiconductors such as Si and Ge and III-V groupcompound-semiconductors such as GaAs, AlGaAs, GaN, InGaN, InSb, GaSb,and AlN may be suitably used as a material for forming the substrate 5.Alternatively, any of II-VI group compound semiconductor materials suchas ZnTe, ZnSe, ZnS, and ZnO may be suitably used as a material forforming the substrate 5. Alternatively, furthermore, any of oxideinsulators such as ZnO, Al₂O₃, SiO₂, TiO₂, CrO2, and CeO₂, nitrideinsulators such as SiN, and plastics may be suitably used as a materialfor forming the substrate 5.

Both two conductors 6 (conductor parts) are formed of a metal film witha triangular top. Furthermore, an example shown in FIG. 2, twoconductors 6 may be substantially equal in shape with a slightdifference in tip angle, width W of the side opposite to the tip, lengthL in the polarization direction P, or the like due to manufacturingvariations or the like. Furthermore, a predetermined corner tip of oneof the paired conductors 6 is arranged facing to the correspondingcorner tip of the other of the paired conductors 6. Then, the tips ofthem are placed apart from each other at a predetermined distance “g”(hereinafter, also referred to as a gap size g) in the X direction(hereinafter, also referred to as a gap direction) in FIG. 1. In otherwords, the paired conductors 6 are arranged in the form of a bow-tie.Thus, as the paired conductors 6 are arranged so that their protruded ortip portions can face to each other, near-field light can be easilygenerated between the paired conductors 6. Furthermore, for instance,such an arrangement of the conductors 6 may be employed as one forheat-assisting magnetic recording using near-field light.

The gap size g between the paired conductors 6 is made sufficientlysmaller than the wavelength of the propagating light Lp. In thisembodiment, furthermore, the gap size g is adjusted to a size equal toor less than a longitudinal length of a recording mark region havingshape anisotropy described later. Furthermore, the gap size g issuitably adjusted to an appropriate one so that near-field light with asufficient strength can be generated between two conductors 6 and thespot diameter of the near-field light can be placed within a rangeappropriate to objective information recording when the propagatinglight Lp from the optical source 1 is irradiated between the twoconductors 6.

In this embodiment, the paired conductors 6 are embedded and formed inone surface of the substrate 5 to even the surfaces of the respectiveconductors 6 and the surface of the substrate 5, thereby providingsmooth transition between them (see FIG. 2B). As a method formanufacturing the near-field light generating unit 4 having such aconfiguration, for example, the following method may be employed. First,hollows are formed in the predetermined areas on the substrate 5, wherethe conductors 6 are to be formed, so that the depth of the hollowedareas will correspond to the thickness t of the conductors 6.Subsequently, a metal film is formed on the surface of the substrate 5where the hollowed areas are formed. Then the metal film is ground untilthe surface of the substrate 5 other than the hollowed areas is exposed.However, the embodiment of the present invention is not limited to sucha process. Alternatively, a pair of conductors 6 (metal films) with apredetermined shape may be formed on the flat surface of the substrate5.

Materials which can be used for preparing the photoconductors 6 includemetals (i.e., Au, Ag, Pt, Cu, Al, Ti, W, Ir, Pd, Mg, and Cr),semiconductors (i.e., Si and GaAs), and materials with goodconductivities such as carbon nanotubes.

[Operation of Near-Field Light Generation and Distribution of FieldIntensity]

The operation of near-field light generation in this embodiment is asfollows: First, propagating light Lp at a predetermined wavelength isemitted from the optical source 1. The propagating light Lp is condensedbetween a pair of conductors 6 of the near-field light generating unit 4through the collimator lens 2 and the condenser lens 3. Therefore,electric charges are intensively distributed on the surface between thepaired conductors 6 and an electric field, or near-field light, isgenerated so as to connect the tips of the respective conductors 6 inpairs. In this embodiment, the near-field light is used as light to beirradiated on a recording medium at the time of recording information onthe recording medium.

In order to check the characteristics of the near-field light generatedbetween the paired conductors 6 as described above, the intensitydistribution (distribution of electric field intensity) of near-fieldlight generated between the paired conductors 6 was investigated by asimulation analysis with the FDTD (Finite Difference Time Domain)method.

FIG. 3 illustrates conditions (materials and dimensions) for thesimulation analysis. In this simulation analysis, the substrate 5 ismade of SiO₂ and the conductors 6 are made of Au. In addition, eachconductor 6 has a width (W) of 440 nm, a length (L) of 220 nm, and athickness (t) of 100 nm. A gap size (g) between the paired conductors 6is 12 nm (also see FIG. 2). In this embodiment, the mid-position betweenthe paired conductors 6 on the plane where the conductors 6 are formedon the substrate 5 is defined as an origin of the coordinates of the Xaxis, the Y axis, and the Z axis.

In this simulation analysis, left-handed polarized propagating light Lpat a wavelength of 780 nm (light having electric field components in theX and Y directions in FIG. 3) is irradiated from the negative side ofthe Z axis to the near-field light generating unit 4. Theinformation-recording side of a recording medium is arranged above thenear-field light generating unit 4 at a distance of 7 nm in the Zdirection (Z=+7 nm) via an air layer. The absolute value of thedielectric constant of the recording medium is sufficiently larger thanthat of the air, so that the component of the electric field in the Zdirection that enters into the recording medium will be very smallaccording to the boundary conditions of the Maxwell's equations.Therefore, in the simulation analysis, attention is only paid on boththe X-direction component and the Y-direction component of the electricfield (Z=+7 nm). The distance between the conductors 6 and theinformation-recording surface (7 mm), which is determined by thesimulation, is one of typical values being assumed now when informationrecording is performed using near-field light.

The results of the simulation analysis are shown in FIG. 4. FIG. 4A is adiagram illustrating both the distribution of the X-direction component|Ex|² and the distribution of the Y-direction component |Ey|² of theelectric field at a position (X, Y, Z)=(x, 0, +7 nm), or any positionalong the X axis (Z=+7 nm). FIG. 4B is a diagram illustrating both thedistribution of the X-direction component |Ex|² and the distribution ofthe Y-direction component |Ey|² of the electric field at a position (X,Y, Z)=(0, y, +7 nm), or any position along the X axis (Z=+7 nm). Here,the characteristic curves of rhomboid marks in FIGS. 4A and 4B representthe distributions of the X-direction component |Ex|². Also, thecharacteristic curves of square marks in FIGS. 4A and 4B represent thedistributions of the Y-direction component |Ey|².

As is evident from FIGS. 4A and 4B, the Y-direction component Ey of theelectric field of the near-field light generated between the pairedconductors 6 is very smaller than the X-direction component Ex thereofand thus the main electric field component of the near-field light is anelectric field component in the X direction, Ex. In other words, thenear-field light generated between the paired conductors 6 has extremelysimilar properties as those of linearly-polarized propagating light inthe direction along which the paired conductors 6 face to each other(gap direction). The above simulation analysis has been described as oneusing circularly-polarized light as the propagating light Lp from theoptical source 1. The same effects as those shown in FIG. 4 can beobtained in the case of using linearly-polarized light Lp insubstantially the same direction as one along which the pairedconductors 6 face to each other (gap direction).

[The Configuration of a Record Reproduction System]

FIG. 5 is a schematic diagram illustrating an exemplary configuration ofa recording/reproducing system when a recording medium is attached onthe recording/reproducing apparatus of the present embodiment. Therecording/reproducing apparatus 11 mainly includes a flying slider head12, a suspension 13 which supports the flying slider head 12, and aspindle 14 that drives the rotation of the recording medium 20.Furthermore, the recording medium 20 is fixed on the rotation axis 15 ofthe spindle 14.

The recording medium 20 of the present embodiment may be a disk-shapedmedium and provided with a plurality of nano-sized recording marks madeof a predetermined recording material. Each recording mark has shapeanisotropy, and 1-bit information is recorded on one recording mark.During the information recording, information is recorded by heatingeach recording mark by near-field light. Materials for forming such arecording mark may be any of recording-layer materials used formagneto-optical recording media, magnetic recording media, phase-changemedia, pigment media, and so on.

FIG. 6 is a schematic diagram illustrating the state of carrying out therecording/reproduction of information by the recording/reproducingapparatus 11 of the present embodiment on which the recording medium 20is attached. In other words, FIG. 6 illustrates the operation of therecording/reproducing system. The recording/reproducing apparatus 11 ofthis embodiment uses a flying slider head 12 for recording informationon the recording medium 20. The slider body 16 of the flying slider head12 is arranged facing the recording medium 20. The recording medium 20may travel at a high speed relative to the flying slider head 12 (in thedirection of the arrow M in FIG. 6). In this case, the relativedisplacement of the slider body 16 is controlled while being lifted at apredetermined flying height from the surface of the recording medium 20by the elastic force of the suspension 13. For example, the spacebetween the recording medium 20 and the conductors 6 may be adjusted to10 nm or less.

The near-field light production section 10, such as one as illustratedin FIG. 1, is mounted on the slider body 16 so that the near-field lightgenerating unit 4 may face the recording medium 20. In this case, thenear-field light generating unit 4 is arranged so that one side thereofon which a pair of the conductors 6 (not shown in FIG. 6) is formed canface the recording medium 20. Furthermore, the optical source 1 (notshown in FIG. 6) may be a semiconductor laser or the like and lightemitted from the optical source 1 is irradiated between the pairedconductors 6 of the near-field light generating unit 4 through awaveguide and so on. As a result, near-field light is generated betweenthe paired conductors 6 to record the information.

Here, if the recording medium is also designed to optically reproduceinformation therefrom, the recording head including the near-field lightgenerating unit 4 may also serve as an information-reproducing head (oneexample thereof will be described in detail in Modified Example 6) ormay be provided separately. In addition, if the recording medium is atype of magnetically reproducing information, a reproduction-only headmay be separately mounted in addition to the recording head having thenear-field light generating unit 4. In the above embodiment, therecording/reproducing apparatus capable of recording and reproducinginformation has been described. However, the embodiment of the presentinvention is not limited to such a recording/reproducing apparatus.Alternatively, for example, the recording head provided with thenear-field light producing section 10 shown in an FIG. 1 may be appliedto an information-recording apparatus which is designed specifically forinformation recording.

[Relationship Between Arrangement of conductors and Arrangement ofRecording Marks]

FIG. 7 illustrates the positional relationship between a pair ofconductors 6 of the near-field light generating unit 4 and recordingmarks formed on the recording medium 20 during the process of recordinginformation on the recording medium 20. Here, an example illustrated inFIG. 7, each recording mark 21 is formed in a rectangle viewed from theside thereof on which near-field light is irradiated (i.e., in thevertical direction of the drawing). Furthermore, in the example shown inFIG. 7, one of the longitudinal direction (L) and the width direction(S) of the recording mark 21 corresponds to the line direction (trackdirection) of the recording medium 20, while the other of thelongitudinal and width directions of the recording mark 21 correspondsto the track-pitch direction of the recording medium 20. In the exampleof FIG. 7, the center positions of the respective recording marks 21 onthe adjacent tracks are aligned in the track-pitch direction.

In this embodiment, the paired conductors 6 are arranged so that the gapdirection (the dashed arrow G in FIG. 7) of the paired conductors 6 ofthe near-field light generating unit 4 can be substantially in parallelwith the longitudinal direction (L) of the recording mark 21 during theprocess of recording information on the recording medium 20.

Referring back to FIG. 4, the main electric field components of thenear-field light 30 generated between the paired conductors 6 are thosein the gap direction (the longitudinal direction of the recording mark21). Therefore, the arrangement of the paired conductors 6 as shown inFIG. 7 allows the near-field light 30 to be efficiently absorbed by therecording marks 21 in the longitudinal direction thereof. As a result,it becomes possible to lower the power of the propagating light Lp fromthe outside (optical source) to increase the temperature of therecording mark 21 to a predetermined level (target temperature). Therelationship between the arrangement of the paired conductors 6 withrespect to the recording mark 21 and the absorption efficiency of theoptical near-field will be described later in detail.

The first embodiment has been described with reference to the example inwhich the arrangement of the paired conductors 6 is shaped like a bowtie on the near-field light generating unit 4. However, the embodimentof the present invention is not limited to such an arrangement.Alternatively, it may be suitably changed to another arrangement, forexample, depending on usage, specifications, or facilitation ofproduction. Hereafter, modified examples of the arrangement of a pair ofconductors 6 will be described.

Modified Example 1

FIG. 8 is a first modified example (Modified Example 1) of thearrangement of paired conductors viewed from above them (the sidethereof facing a recording medium). In this modified example 1, twoconductors 56 are configured and arranged to form a so-called adouble-rod shape. These two conductors 56 (conductor part) have the sameconfiguration and the sides thereof facing the recording medium have arectangular shape. Furthermore, the conductors 56 are arranged so thatone narrow side of one thereof can face one narrow side of the otherthereof.

In the modified example illustrated in FIG. 8, the direction along whichthe narrow sides of the respective conductors 56 are facing to eachother (the direction along the long side of the conductor 56) is definedas an X direction. In contrast, the direction perpendicular to the Xdirection (the direction along the narrow side) is defined as a Ydirection. Furthermore, the thickness direction of the conductor 56 isdefined as a Z direction.

Furthermore, the gap size g is adjusted so that near-field light with asufficient strength can be generated between two conductors 56 and thespot diameter of the near-field light can be placed within a rangeappropriate to objective information recording when the propagatinglight Lp from an optical source is irradiated between the two conductors6. During the process of recording information on the recording medium20, the direction along which two conductors 56 face to each other (thegap direction) substantially corresponds to the longitudinal directionof a recording mark having shape anisotropy formed on the recordingmedium.

Here, in the configuration of the modified example 1, like the firstembodiment, the distribution of electric field intensity of near-fieldlight 30 generated between the paired conductors 56 is also investigatedby the simulation analysis using the FDTD method.

FIG. 9 illustrates conditions (materials and dimensions) for thesimulation analysis. In this simulation analysis, the substrate 55 ismade of SiO₂ and the conductors 56 are made of Au. In addition, eachconductor 56 has a width (W) of 20 nm, a length (L) of 60 nm, and athickness (t) of 50 nm. A gap size (g) between the paired conductors 56is 12 nm. Other simulation conditions are similar to those of the firstembodiment. In this embodiment, the mid-position between the pairedconductors 56 on the plane where the conductors 56 are formed on thesubstrate 55 is defined as an origin of the coordinates of the X axis,the Y axis, and the Z axis.

The results of the simulation analysis are represented in FIG. 10. FIG.10A is a diagram illustrating both the distribution of the X-directioncomponent |Ex|² and the distribution of the Y-direction component |Ey|²of the electric field at a position (X, Y, Z)=(x, 0, +7 nm), or anyposition along the X axis (Z=+7 nm). FIG. 10B is a diagram illustratingboth the distribution of the X-direction component |Ex|² and thedistribution of the Y-direction component |Ey|² of the electric field ata position (X, Y, Z)=(0, y, +7 nm), or any position along the Y axis(Z=+7 nm). Here, the characteristic curves of rhomboid marks in FIGS.10A and 10B represent the distributions of the X-direction component|Ex|². Also, the characteristic curves of square marks in FIGS. 10A and10B represent the distributions of the Y-direction component |EY|².

As is evident from FIGS. 10A and 10B, in the configuration of the firstmodified example, the Y-direction component Ey of the electric field ofthe near-field light generated between the paired conductors 56 is verysmaller than the X-direction component Ex thereof and thus the mainelectric field component of the near-field light is an electric fieldcomponent in the X direction, Ex. In other words, just as in the casewith the first embodiment, the near-field light generated between thepaired conductors 56 of the first modified example has extremely similarproperties as those of linearly-polarized propagating light in thedirection along which the paired conductors 56 face to each other (gapdirection).

Modified Example 2

FIG. 11 is a schematic diagram illustrating the configuration of the topof a conductor (the side thereof facing to a recording medium) accordinga second modified example (Modified Example 2) of the present invention.The conductor 66 of the second modified example is of a so-calledbow-tie slot type.

In this second modified example, an opening 67 is formed in the centerof the conductor 66, where no metal film is formed. Two sides of theopening 67, which are opposite to each other in the X direction in FIG.11, are protruded as a triangle (convex shape) and their sides facingeach other are symmetrical with each other in the Y direction. On theother hand, two other sides of the opening 67, which are opposite toeach other in the Y direction, are linear and in parallel with eachother. In other words, the bow-tie-shaped opening 67 is formed in thecenter of the conductor 66 by two conductor parts 66 a, each of which isformed of a triangle shape that defines opposite side portions of theopening 67 in the X direction, and two conductor-connecting parts 66 bthat connect two conductor parts 66 a.

Furthermore, the gap size g is adjusted so that near-field light with asufficient strength can be generated between two conductor parts 66 aand the spot diameter of the near-field light can be placed within arange appropriate to objective information recording when thepropagating light Lp from an optical source is irradiated between thetwo conductor parts 66 a. During the process of recording information onthe recording medium 20, the direction along which two conductor parts66 a face to each other (the gap direction) substantially corresponds tothe longitudinal direction of a recording mark having shape anisotropyformed on the recording medium.

Here, in the configuration of the modified example 2, like the firstembodiment, the distribution of electric field intensity of near-fieldlight 30 generated between the paired conductor parts 66 a is alsoinvestigated by the simulation analysis using the FDTD method.

FIG. 12 illustrates conditions (materials and dimensions) for thesimulation analysis. In this simulation analysis, the substrate 65 ismade of SiO₂ and the conductor 66 is made of Au. Furthermore, thebow-tie-shaped opening 67 has a width of 200 nm in the X direction and awidth of 200 nm in the Y direction. The gap size g between two conductorparts 66 a is 12 nm. In addition, the thickness of the conductor 66 is100 nm. Other simulation conditions are similar to those of the firstembodiment. In this embodiment, the mid-position between the pairedconductor parts 66 a on the plane where the conductor 66 is formed onthe substrate 65 is defined as an origin of the coordinates of the Xaxis, the Y axis, and the Z axis.

The results of the simulation analysis are represented in FIG. 13. FIG.13A is a diagram illustrating both the distribution of the X-directioncomponent |Ex|² and the distribution of the Y-direction component |Ey|²of the electric field at a position (X, Y, Z)=(x, 0, +7 nm), or anyposition along the X axis (Z=+7 nm). FIG. 13B is a diagram illustratingboth the distribution of the X-direction component |Ex|² and thedistribution of the Y-direction component |Ey|² of the electric field ata position (X, Y, Z)=(0, y, +7 nm), or any position along the Y axis(Z=+7 nm). Here, the characteristic curves of rhomboid marks in FIGS.13A and 13B represent the distributions of the X-direction component|Ex|². Also, the characteristic curves of square marks in FIGS. 13A and13B represent the distributions of the Y-direction component |EY|².

As is evident from FIGS. 13A and 13B, in the configuration of the secondmodified example, the Y-direction component Ey of the electric field ofthe near-field light generated between the paired conductor parts 66 ais very smaller than the X-direction component Ex thereof and thus themain electric field component of the near-field light is an electricfield component in the X direction, Ex. In other words, just as in thecase with the first embodiment, the near-field light generated betweenthe paired conductor parts 66 a in the second modified example hasextremely similar properties as those of linearly-polarized propagatinglight in the direction along which the paired conductor parts 66 a faceto each other (gap direction).

Modified Example 3

FIG. 14 is a schematic diagram illustrating the configuration of the topof a conductor (the side thereof facing to a recording medium) accordinga third modified example (Modified Example 3) of the present invention.The conductor 76 of the third modified example is of a so-calledC-aperture type. In this second modified example, an opening 77 isformed in the center of the conductor 76, where no metal film is formed.Two sides of the opening 77 are opposite to each other in the Xdirection in FIG. 14. One of these sides is protruded toward theopposite side which is formed linearly. On the other hand, two othersides of the opening 77, which are opposite to each other in the Ydirection, are linear and in parallel with each other. In other words,the C-shaped opening 77 is formed in the center of the conductor 76 bytwo conductor parts 76 a and 76 c, which defines two side portionsfacing to each other in the X direction, and two conductor-connectingparts 76 b that connect two conductor parts 76 a and 77 c, which definestwo side portions facing to each other in the Y direction.

Furthermore, the gap size g is adjusted so that near-field light with asufficient strength can be generated between two conductor parts 76 aand 76 c when the propagating light Lp from an optical source isirradiated between the two conductor parts 76 a and 76 c. Furthermore,the gap size g between two conductors 76 a and 76 c is adjusted so thatthe spot diameter of the near-field light can be placed within a rangeappropriate to objective information. During the process of recordinginformation on the recording medium 20, the direction along which twoconductor parts 76 a and 76 c face to each other (the gap direction)substantially corresponds to the longitudinal direction of a recordingmark having shape anisotropy formed on the recording medium.

Here, in the configuration of the modified example 3, like the firstembodiment, the distribution of electric field intensity of near-fieldlight 30 generated between the paired conductor parts 76 a and 76 c isalso investigated by the simulation analysis using the FDTD method.

FIG. 15 illustrates conditions (materials and dimensions) for thesimulation analysis. In this simulation analysis, the substrate 75 ismade of SiO₂ and the conductor 76 is made of Au. Furthermore, theC-shaped opening 77 has a width of 26 nm in the X direction and a widthof 400 nm in the Y direction. The protruded portion of the conductorpart 76 a has a width of 20 nm. Furthermore, the gap size g between twoconductor parts 76 a and 76 c is 12 nm and the thickness of theconductor 76 is 50 nm. Other simulation conditions are similar to thoseof the first embodiment. In this embodiment, the mid-position betweenthe paired conductor parts 76 a and 76 c on the plane where theconductor 76 is formed on the substrate 75 is defined as an origin ofthe coordinates of the X axis, the Y axis, and the Z axis.

The results of the simulation analysis are represented in FIG. 16. FIG.16A is a diagram illustrating both the distribution of the X-directioncomponent |Ex|² and the distribution of the Y-direction component |Ey|²of the electric field at a position (X, Y, Z)=(x, 0, +7 nm), or anyposition along the Y axis (Z=+7 nm). FIG. 16B is a diagram illustratingboth the distribution of the X-direction component |Ex|² and thedistribution of the Y-direction component |Ey|² of the electric field ata position (X, Y, Z)=(0, y, +7 nm), or any position along the Y axis(Z=+7 nm). Here, the characteristic curves of rhomboid marks in FIGS.16A and 16B represent the distributions of the X-direction component|Ex|². Also, the characteristic curves of square marks in FIGS. 16A and16B represent the distributions of the Y-direction component |Ey|².

As is evident from FIGS. 16A and 16B, in the configuration of the thirdmodified example, the Y-direction component Ey of the electric field ofthe near-field light generated between the paired conductor parts 76 aand 76 b is very smaller than the X-direction component Ex thereof. Inother words, the near-field light is an electric field component in theX direction, Ex, just as in the case with the first embodiment, thenear-field light generated between two conductor parts 76 a and 76 c inthe third modified example has extremely similar properties as those oflinearly-polarized propagating light in the direction along which twoconductor parts 76 a and 76 c face to each other.

In any of the configurations of the above Modified Examples 1 to 3,near-field light generated between two conductor parts (or conductors)becomes linearly-polarized light in the gap direction of these twoconductive parts. In other words, the near-field light generated betweentwo conductors (or conductor parts) of any of the above ModifiedExamples 1 to 3 has similar properties as those of the near-field lightgenerated in the first embodiment. Therefore, in any of ModifiedExamples 1 to 3, the near-field light can be efficiently absorbed by therecording marks just as in the case with the first embodiment.

[Relationship Between Arrangement of Conductors and AbsorptionEfficiency of Near-Field Light]

Here, the relationship between the arrangement of conductors thatgenerate near-field light and the absorption efficiency of near-fieldlight on recording mark (irradiation target) will be described indetail.

First, the relationship between the polarization direction of light (theplane wave of linearly polarized light is represented by the arrow Lw inFIG. 17) to be irradiated on a recording mark having shape anisotropyand the optical absorption efficiency was investigated by simulationanalysis. Specifically, optical absorption efficiency was evaluated bycalculating an increase in temperature of a recording mark when apredetermined amount of light was irradiated thereon for a predeterminedtime and the evaluation was then repeated with difference polarizationdirections.

FIG. 17 illustrates conditions (materials and dimensions) for thesimulation analysis. In this simulation analysis, a substrate 23 is madeof SiO₂ and recording marks 24 (irradiation targets) formed on thesubstrate 23 are made of Co. Furthermore, the width (Wm) of therecording mark 24 (the width thereof in the width direction) is definedas Wm=20 nm and the thickness (tm) thereof is defined as tm=10 nm. Inthis simulation analysis, the width (Wm) of the recording mark 24 isfixed, while the length (Lm) thereof (the width thereof in thelongitudinal direction) is changed variously. The aspect ratio (Lm/Wm)of the recording mark 24 is changed variously. Changes in opticalabsorption efficiency with different aspect ratios of the recording markwere investigated. In this case, however, the length (Lm) of therecording mark 24 is much smaller than the wavelength of the irradiatedlight.

Furthermore, the simulation analysis was performed on two cases: one inwhich the polarization direction of light irradiated on the recordingmark 24 corresponded to the longitudinal direction of the recording mark24 (the X direction in FIG. 17); and the other in which the polarizationdirection of light irradiated on the recording mark 24 corresponded tothe width direction of the recording mark 24 (the Y direction in FIG.17).

The results of the simulation analysis are shown in FIG. 18. In FIG. 18,the horizontal axis represents the aspect ratio of the recording mark 24and the vertical axis represents the amount of rise in temperature ofthe recording mark 24. Furthermore, the characteristic curve of rhomboidmarks in FIG. 18 represents changes in amount of rise in temperaturewhen light polarized in the X direction (longitudinal direction) isirradiated on the recording mark 24, while the characteristic curve ofsquare marks represents changes in amount of rise in temperature whenlight polarized in the Y direction (width direction) is irradiated onthe recording mark 24. In FIG. 18, furthermore, the characteristicfeature of the recording mark with shape isotropy (aspect ratio=1) isalso plotted for comparison.

As is evident from the characteristic curves represented in FIG. 18, theamount of rise in temperature is constant irrespective of thepolarization direction of light when the recording mark with anisotropic shape (aspect ratio=1) is used. In contrast, in the case ofthe recording mark with shape anisotropy (aspect ratio>1), the amount ofrise in temperature varies depending on the polarization direction ofthe irradiated light. Specifically, the case in which the polarizationdirection of the irradiated light corresponds to the longitudinaldirection of the recording mark (in parallel with each other) leads tomore rise in temperature of the recording mark, compared with the casein which both directions are perpendicular to each other. As a result,it is found that the optical absorption efficiency of the recording markcan be increased by arranging the longitudinal direction of therecording mark in substantially parallel with the polarization directionof the irradiated light.

As described above, the near-field light generated between two conductorparts (or conductors) described in any of the above Embodiment 1 andModified Examples 1 to 3 has extremely similar properties as those ofsubstantially, linearly-polarized propagating light in the gap directionof two conductor parts. Therefore, from the results of the analysis inFIG. 18, it becomes possible to improve the optical absorptionefficiency of the recording mark by making the gap direction of twoconductor parts in parallel with the longitudinal direction of therecording mark.

To confirm such an effect, the amount of rise in temperature of therecording mark 24 was calculated by a simulation analysis when thenear-field light generated by the configuration of conductors of any ofEmbodiment 1, Modified Example 1, and Modified Example 3 was irradiatedon the recording mark 24 as shown in FIG. 17. Since the characteristicproperties of the near-field light (FIG. 13) generated by theconfiguration of Modified Example 2 are substantially the same as thoseof the near-field light (FIG. 4) generated by the configuration ofEmbodiment 1. Therefore, the configuration of Modified Example 2 willnot be subjected to the simulation analysis.

FIG. 19 illustrates conditions (materials and dimensions) for thesimulation analysis. In this simulation analysis, a substrate 25 is madeof SiO₂ and recording marks 26 formed on the substrate 25 are made ofCo. The direction of the main electric field component of near-fieldlight 30 as irradiated light (gap direction) corresponds to the Xdirection in FIG. 19. Propagating light, which is irradiated from theoptical source to between two conductor parts (or conductors), isirradiated on conductor parts (or conductors) at a predetermined amountof light for 0.1 nsec.

In addition, the thickness (tm) of the recording mark 26 is set to tm=10nm. In this simulation analysis, the length (Lm) of the recording mark26 is set to Lm=20 nm and the width (Wm) thereof is set to Wm=8 nm. Thedirection of the main electric field component of near-field light 30(gap direction) corresponded to the longitudinal direction of therecording mark 26. For comparison, the same calculation was performed onthe recording mark 26 of different dimensions, Lm=8 nm and Wm=20 nm(Comparative Example). In the comparative example, the length (Lm) ofthe recording mark 26 is shorter than the width (Wm) thereof, so thatthe main electric field component of near-field light 30 (gap direction)can be perpendicular to the longitudinal direction of the recording mark26. The results of this simulation analysis are illustrated in Tables 1and 2 below.

TABLE 1 Absolute value of amount of rise in temperature (° C.)Near-field light generating unit First Modified Modified EmbodimentExample 1 Example 3 Gap direction// 3601 839 26 longitudinal directionLm = 20 nm, Wm = 8 nm Gap direction 633 161 12 ⊥ longitudinal directionLm = 8 nm, Wm = 20 nm

TABLE 2 Relative value of amount of rise in temperature (⊥ standard)Near-field light generating unit First Modified Modified EmbodimentExample 1 Example 3 Gap direction// 5.7 5.2 2.2 longitudinal directionLm = 20 nm, Wm = 8 nm Gap direction 1.0 1.0 1.0 ⊥ longitudinal directionLm = 8 nm, Wm = 20 nm

The values in the column of “Gap direction//Longitudinal direction”represent the amounts of rise in temperature when the direction alongwhich two conductor parts (or conductors) face to each other (the gapdirection) corresponds to the longitudinal direction of the recordingmark 26. In addition, the values in the column of “Gap direction ⊥Longitudinal direction” represent the amounts of rise in temperaturewhen the direction along which two conductor parts (or conductors) faceto each other (the gap direction) is perpendicular to the longitudinaldirection of the recording mark 26. In addition, Table 2 represents arelative ratio of amounts of rise in temperature with reference to theamount of rise in temperature of the comparative example.

As is evident from the above Tables 1 and 2, it is found that theoptical absorption efficiency can be improved by an increase in amountof rise in temperature of the recording mark as a result of allowing thegap direction of two conductor parts to substantially correspond to thelongitudinal direction of the recording mark.

Modified Example 4

As shown in FIG. 7, the first embodiment has been described withreference to the example in which the center positions of the respectiverecording marks 21 are aligned in the track-pitch direction. However,the embodiment of the present invention is not limited to such anexample. Alternatively, for example, the center positions of therespective recording marks on the tracks adjacent to each other may bestaggered in the track-pitch direction. An example of such anarrangement is illustrated in.

FIG. 20 is an enlarged top view of part of an region where recordingmarks are formed. An example of the recording medium shown in FIG. 20includes recording marks 27 made of a predetermined recording materialand formed in a rectangular shape are arranged at a predeterminedspacing in both the line direction Ld and the track-pitch direction T ofthe recording medium. In this case, the center positions 27 a of therespective recording marks 27 on the adjacent tracks are staggered(dashed lines d1 and d2) in the track-pitch direction T (the center ofeach track is represented by the dashed line d3). Therefore, such anarrangement of the recording marks 27 may lead to further reduction intrack pitch.

In the example illustrated in FIG. 20, furthermore, the line directionof the recording medium corresponds to the width direction of therecording mark 27, while the track-pitch direction of the recordingmedium corresponds to the longitudinal direction of the recording mark27. However, the embodiment of the present invention is not limited tosuch an arrangement. Alternatively, for example, the line direction Ldof the recording medium may correspond to the longitudinal direction ofthe recording mark 27, while the track-pitch of the recording medium maycorrespond to the width direction of the recording mark 27.

Modified Example 5

Each of the first embodiment and the fourth modified example has beendescribed with reference to the example in which the recording medium isformed in a rectangular shape viewed from the direction of irradiatingnear-field light. However, the embodiment of the present invention isnot limited to such a shape. Alternatively, the recording mark may haveany shape as long as it retains shape anisotropy in the direction ofirradiating the near-field light. An example of such a case isillustrated in FIG. 21. Here, FIG. 21 is a diagram illustrating theexample in which a recording mark 28 is formed in an elliptical shapeviewed from the direction of irradiating near-field light.

In the example illustrated in FIG. 21, the line direction Ld of therecording medium corresponds to the width direction of the recordingmark 28 and the track-pith direction T of the recording mediumcorresponds to the longitudinal direction of the recording mark.However, the embodiment of the present invention is not limited to suchan arrangement. Alternatively, for example, the line direction of therecording medium may correspond to the longitudinal direction of therecording mark 28, while the track-pitch of the recording medium maycorrespond to the width direction of the recording mark 28. Although theexample of FIG. 21 shows the example arranged by the center positions 28a of the respective recording marks 28 on the adjacent tracks arestaggered (dashed lines d1 and d2) in the track-pitch direction T.However, the embodiment of the present invention is not limited to suchan arrangement. Alternatively, the center positions 28 a of therespective recording marks 28 on the adjacent tracks may be aligned inthe track pitch direction T.

Modified Example 6

The above first embodiment has been described with reference to theexample in which the near-field light producing section 10 thatgenerates near-field light is mounted on the recording head. However,the embodiment of the present invention is not limited to such aconfiguration. Alternatively, in the case of optically reproducinginformation from a recording medium, if the recording medium is alsodesigned to optically reproduce information therefrom, the recordinghead including the near-field light producing section 10 may also serveas an information-reproducing head. In the sixth modified example, anexample of such a configuration will be described.

FIG. 22 is a schematic diagram illustrating an exemplary configurationof a recording/reproducing system when a recording medium is attached onthe recording/reproducing apparatus of the sixth embodiment. Therecording/reproducing apparatus 80 of the sixth modified example isconfigured in a manner similar to that of the first embodiment, exceptof a recording/reproducing head 85 that performs recording/reproductionof information. In FIG. 22, the same components as those in the abovefirst embodiment (FIG. 5) are assigned the same reference numerals.

The schematic configuration of the recording/reproducing head 85 isillustrated in FIG. 23. In Modified Example 6, the recording/reproducinghead 85 includes a flying slider unit 81 supported by a suspension 13and an optical system 82 that irradiates propagating light Lp on theflying slider unit 81, which are configured separately. Alternatively,the flying slider unit 81 and the optical system 82 may be integrallyconfigured and held by the suspension 13.

The flying slider unit 81 (near-field light generating unit) includes anoptically transparent substrate 87 and two conductors 86 formed on oneside (the top) of the substrate 87. Here, the shape, arrangement, and soon of the paired conductors 86 may be the same as those of the firstembodiment (see FIG. 2). In this case, the flying slider unit 81 isarranged so that one side thereof on which a pair of the conductors 86is formed can face a recording medium 20. When the recording medium 20travels at a high speed relative to the flying slider unit 81, therelative displacement of the flying slider unit 81 is adjusted whilebeing lifted at a predetermined flying height from the surface of therecording medium 20 by the elastic force of the suspension 13.Subsequently, propagating light Lp is incident on the other side of thesubstrate 87, which is opposite to the side thereof on which the pairedthe conductors 86 are formed, and an optically near-field is thengenerated between the paired conductors 86.

In this sixth modified example, the paired conductors 86 are arranged sothat the direction (the X direction in FIG. 23) along which the pairedconductors 86 of the flying slider unit 81 face to each other can besubstantially in parallel with the longitudinal direction of a recordingmark having shape anisotropy during the process of recording informationon the recording medium 20.

The optical system 82 is provided with a recording system that performsinformation recording on the recording medium 20. Here, the recordingsystem mainly includes an optical source 61, a condensing element 92,and a beam splitter 93, where the condensing element 92 is constructedof a condenser lens 92 and so on. Light emitted from the optical source91 enters into the flying slider unit 81 via condensing element 92 andthe beam splitter 93. As a result, the incident light causes thegeneration of near-field light between the paired conductors 86 to heatthe recording mark on the recording medium 20. Therefore, the recordingmark can be efficiently heated as the direction along which the pairedconductors 86 face to each other substantially corresponds to thelongitudinal direction of the recording mark.

Furthermore, the optical system 82 is provided with a reproducing systemthat performs information reproduction in response to light reflectedfrom the recording medium 20. The reproducing system mainly includes apolarizer 94, a condensing element 95, and a light reception unit 96.The polarizer 94, the condensing element 95, and the light receptionunit 96 are arranged in this order from the beam splitter 93. Lightreflected from the recording medium 20 is separated from the incidentlight by the beam splitter 93 and then incident on the polarizer 94. Thelight passed through the polarizer 94 enters into the light receptionunit 96 through the condensing element 95. Subsequently, the informationis reproduced from the recording medium 20 on the basis of the lightreflected therefrom and entered into the light reception unit 96.

Each of the first embodiment 1 and the sixth modified example has beendescribed with reference to the example in which the head is of aflying-slider type. However, the embodiment of the present invention isnot limited to such a type of the head. Alternatively, for example, theheight of the head may be adjusted by an actuator or the like.

2. Second Embodiment

The near-field light production section of the recording/reproducingapparatus described in the first embodiment is able to generate a strongnear-field light by making the size of a gap between a pair ofconductors sufficiently smaller than the wavelength of propagating lightemitted from an optical source. In the first embodiment, however, achange in gap size between the paired conductors leads to a change inshape of the generated near-field light and a change in strength of thenear-field light irradiated on the recording medium. To efficientlyirradiate near-field light at a higher strength during the informationrecording, it is necessary to optimally adjust the relationship betweenthe gap size between the paired conductors and the distance between therecording head and the recording medium. In the second embodiment, forfurther optimizing their relationship, both the configuration of therecording/reproducing apparatus and the configuration of therecording/reproducing system will be described on the basis of those ofthe first embodiment.

[Configuration of Recording/Reproducing Apparatus]

FIG. 24A is a diagram schematically illustrating the configuration of arecording/reproducing system which is employed during the process ofinformation recording on a recording medium attached on therecording/reproducing apparatus of the present embodiment. In FIG. 24A,the same components as those in the above first embodiment (FIG. 5) areassigned the same reference numerals.

As is evident from the comparison between FIG. 24A and FIG. 5 (firstembodiment), the recording/reproducing system employed when therecording medium is attached on the recording/reproducing apparatus ofthe present embodiment is generally configured in a manner similar tothat of the first embodiment. In this embodiment, however, therelationship between the gap size between the paired conductors and thedistance between the recording head and the recording medium during theinformation recording. Therefore, the description of each component inthe recording/reproducing apparatus and the recording/reproducing systemwill be omitted in the following description, but the relationshipbetween the gap size between the paired conductors and the distancebetween the recording head and the recording medium during theinformation recording will be described. In this embodiment, theconductors are configured and arranged in a manner similar to those ofthe first embodiment (see FIG. 2).

FIG. 24B illustrates an enlarged cross-sectional view of region Bsurrounded by a dotted line in FIG. 24A. In the example illustrated inFIG. 24B, recording marks 21 and a protective film 20 b are formed on asubstrate 20 a of a recording medium 20. Here, for example, theprotective film 20 b may be formed of a diamond-like carbon film.

In the present embodiment, the protective film 20 b of the recordingmedium 20 faces one side of the near-field light generating unit 4mounted on the flying slider head 12, on which conductors 6 are formed,through an air layer 100. In addition, during the information recording,the direction along which paired conductors 6 face to each other (the Xdirection in FIG. 24B) is substantially in parallel with thelongitudinal direction of the recording mark 21 just as in the case withthe first embodiment.

In the present embodiment, the flying height of the flying slider head12 is adjusted (controlled) so that the following mathematicalexpression 1 can be established in the relationship between the gap size(g) between the paired conductors 6 and the distance z between theconductors 6 and the recording marks 21 during the information recording(during the stable flying of the flying slider head 12).g=√{square root over (2)}−z  [Mathematical expression 1]

If the relation of the above mathematical expression 1 is establishedduring the information recording, then the maximum field intensity ofnear-field light irradiated on the recording mark 21 is attained. Thus,the near-field light can be efficiently irradiated on the recording mark21. Hereinafter, a principle of deriving the above mathematicalexpression 1 will be described with reference to FIGS. 25 to 27.

FIG. 25 illustrates an enlarged cross-sectional view of a region wherethe flying slider head 12 and the recording medium 20 face to each otherduring the information recording. In FIG. 25, in order to simplifyexplanation, the protective film 20 b shown in FIG. 24B is omitted. Inaddition, for convenience of explanation, the up-and-down positionalrelationship between the flying slider head 12 and the recording medium20 in FIG. 25 is reversed from that of FIG. 24B because of explaining aprinciple of deriving the above mathematical expression 1. In thisembodiment, the mid-position between the paired conductors 6 on theplane is defined as an origin (“0 (zero)” in FIG. 25) of the coordinatesof the X direction (the direction along which two conductors 6 face toeach other), the Y direction (perpendicular to the drawing of FIG. 25),and the Z direction.

As shown in FIG. 25, at given time in the information recording, it isconsidered that positive electric charges are induced near the surfaceof the conductor 6 at a position of X=+g/2 when the conductor 6 isplaced in the “+X” direction; and negative electric charges are inducednear the surface of the conductor 6 at a position of X=−g/2 when theconductor 6 is placed in the “−X” direction. Since the propagating lightLp irradiated from the optical source to between the paired conductors 6is high-frequency light, the polarity of charges induced near thesurface at a position of X=±g/2 can be alternately changed from positiveto negative and vice versa in response to the frequency of thepropagating light Lp irradiated between the paired conductors 6.

Under the conditions illustrated in FIG. 25, the induced electriccharges spread and exist on the limited areas on the surfaces of therespective conductors 6. However, such an area is very small, so thatthe area of induced electric charges can be equivalently represented bypoint charges. In other words, in the example illustrated in FIG. 25,such an arrangement is equivalent to the case in which positive andnegative point charges are arranged on the surfaces of the respectiveconductors 6 at positions of X=+g/2 and −g/2 in stead of the conductors6.

FIG. 26 is a schematic diagram in which the state of the inducedelectric charges in FIG. 25 is equivalently represented by pointcharges. The state shown in FIG. 25 is equivalent to an arrangement ofpoint charges 71 and 72, where a point charge of +q 71 is arranged at aposition of (X, Y, Z)=(+g/2, 0, 0), while a point charge of −q 72 isarranged at a position of (X, Y, Z)=(−g/2, 0, 0). In the exampleillustrated in FIG. 26, furthermore, the amount of charge induced on thesurface of each conductive substrate 6 is defined as “q”.

Hereinafter, the above mathematical expression 1 will be derived withreference to the configuration illustrated in FIG. 26. The area to beconsidered about near-field light is considerably smaller than thewavelength of the propagating light Lp from the optical source. In thisarea, therefore, the above mathematical expression 1 may be calculatedwhile electro-statically making approximation with a case that there isno phase lag of electromagnetic waves in the area.

The respective directional components E_(x), E_(y), and E_(z) of theelectric field (near-field light) at a position of (X, Y, Z)=(x, y, z)where the point charge 71 (+q) and the point charge 72 (−q) aregenerated can be represented by the following mathematical expression 2.Here, ∈₀ in the following mathematical expression 2 is a dielectricconstant of the surroundings of the point charges 71 and 72 (air layer100).

$\begin{matrix}{{{X\mspace{14mu}{{component}:E_{x}}} = {\frac{q}{8 \cdot \pi \cdot ɛ_{0}} \cdot \begin{pmatrix}{\frac{{2x} - g}{\left( {x^{2} - {xg} + {\frac{1}{4}g^{2}} + y^{2} + z^{2}} \right)^{3/2}} -} \\\frac{{2x} - g}{\left( {x^{2} + {xg} + {\frac{1}{4}g^{2}} + y^{2} + z^{2}} \right)^{3/2}}\end{pmatrix}}}{{Y\mspace{14mu}{{component}:E_{x}}} = {\frac{q}{4 \cdot \pi \cdot ɛ_{0}} \cdot \begin{pmatrix}{\frac{y}{\left( {x^{2} - {xg} + {\frac{1}{4}g^{2}} + y^{2} + z^{2}} \right)^{3/2}} -} \\\frac{y}{\left( {x^{2} + {xg} + {\frac{1}{4}g^{2}} + y^{2} + z^{2}} \right)^{3/2}}\end{pmatrix}}}{{Z\mspace{14mu}{{component}:E_{z}}} = {\frac{q}{4 \cdot \pi \cdot ɛ_{0}} \cdot \begin{pmatrix}{\frac{z}{\left( {x^{2} - {xg} + {\frac{1}{4}g^{2}} + y^{2} + z^{2}} \right)^{3/2}} -} \\\frac{z}{\left( {x^{2} + {xg} + {\frac{1}{4}g^{2}} + y^{2} + z^{2}} \right)^{3/2}}\end{pmatrix}}}} & \left\lbrack {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In addition, the directional components of an electric field in the airlayer 100 are defined as E_(x0), E_(y0), and E_(z0), respectively. Also,the directional components of an electric field in a recording mark 21(the irradiation target of near-field light) are defined as E_(x1),E_(y1), and E_(z1), respectively. Furthermore, if the dielectricconstant of the recording mark 21 is defined as ∈1 and the boundarysurface between the air layer 100 and the recording mark 21 is inparallel with the XY plane, then the following mathematical expression 3is established based on the boundary conditions of the Maxwell'sequations.

$\begin{matrix}{{E_{x\; 0} = E_{x\; 1}}{E_{y\; 0} = E_{y\; 1}}{E_{z\; 0} = {\frac{ɛ_{1}}{ɛ_{0}}E_{z\; 1}}}} & \left\lbrack {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 3} \right\rbrack\end{matrix}$

Here, the first and second equations in the above mathematicalexpression 3 represent that the field components E_(x) and E_(y), whichare parallel to the boundary surface, are contiguous on the boundarybetween different media. In addition, the third equation of the abovemathematical expression 3 represents that the field component Ez, whichis perpendicular to the boundary surface, is discontinuous on theboundary between different media.

Here, it is considered that information is recorded at a position of (X,Y, Z)=(0, 0, z) (X-marked position in FIG. 26) on the recording mark 21which faces the mid-position (origin) between two conductors 6. In thiscase, both the Y-direction component E_(y) and the Z-direction componentE_(z) of the electric field becomes 0 (zero) in the above mathematicalexpression 1. It becomes. On the other hand, the X-direction componentEx is represented by the following mathematical expression 4:

$\begin{matrix}{E_{x} = {{- \frac{q}{4 \cdot \pi \cdot ɛ_{0}}} \cdot \frac{g}{\left( {{\frac{1}{4}g^{2}} + z^{2}} \right)^{3/2}}}} & \left\lbrack {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 4} \right\rbrack\end{matrix}$

The above mathematical expression 4 is used for obtaining the conditionsfrom which the electric field intensity, or the near-field lightintensity (absolute value) reaches its maximum at aninformation-recording position of (X, Y, Z)=(0, 0, z). In this recordingposition, the above mathematical expression 4 represents only theX-direction component Ex among the components of the electric field.Furthermore, as represented by the above mathematical expression 3, theX-direction component E_(x) of the electric field is contiguous on theboundary surface without being affected by the difference between thedielectric constants of the inside and outside of the boundary surfacebetween the air layer 100 and the recording mark 21. Thus, thedielectric constant ∈₀ of the air layer 100 in the above mathematicalexpression 4 may be provided as an invariable. As a result, the abovemathematical expression 4 can be rewritten as described below. In thefollowing mathematical expression 5, “A” represents an invariable.

$\begin{matrix}{E_{x} = {A \cdot \frac{g}{\left( {{\frac{1}{4}g^{2}} + z^{2}} \right)^{3/2}}}} & \left\lbrack {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Here, variable portions other than the invariable A on the right-handside of the above mathematical expression 5 are collectively replacedwith “f”. That is, the variable “f” is represented by the followingmathematical expression 6:

$\begin{matrix}{f = \frac{g}{\left( {{\frac{1}{4}g^{2}} + z^{2}} \right)^{3/2}}} & \left\lbrack {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 6} \right\rbrack\end{matrix}$

In the above mathematical expression 6, if the distance between therecording mark 21 and the conductor 6 is 7 nm (z=7 nm), the variable fvaries as illustrated in FIG. 27 with respect to the gap size g betweenthe conductors 6. As is evident from FIG. 27, the variable f reaches itsmaximum when the gap size g reaches a predetermined size. In addition,the field intensity (near-field light intensity) reaches its maximum atthe maximum value of the variable f.

The condition that the variable f reaches its maximum is obtained bycalculating df/dg=0 in the above mathematical expression 6 and thefollowing mathematical expression 7, which is the same as themathematical expression 1, is obtained.g=√{square root over (2)}−z  [Mathematical expression 7]

As described above, the above mathematical expression 1 is derived.Furthermore, if the maximum value of the variable f is defined as fm,the gap size corresponding to the maximum value fm is defined as gm, andthe variable f on the vertical axis and the variable g on the horizontalaxis in FIG. 27 are converted into Δ(=f/fm) and α(=g/gm), when z=+7 nm,then the characteristics chart of FIG. 27 can be represented as onerepresented in FIG. 28. Furthermore, the relational expression of boththe variable Δ and the variable α shown in FIG. 28 can be expressed bythe following mathematical expression 8.

$\begin{matrix}{\Delta = \frac{3\alpha\sqrt{3}}{\left( {\alpha^{2} + 2} \right)^{3/2}}} & \left\lbrack {{Mathematical}\mspace{14mu}{expression}\mspace{14mu} 8} \right\rbrack\end{matrix}$

The above mathematical expression 8 is employed to find the range of thegap size g that allows the variable Δ to reach about 60% (Δ=0.6) of Δ=1(100%) in FIG. 28. As a result, it is found that such a gap size is inthe range of about 0.5071 z to 3.286 z. In other words, if the gap sizeg between two conductors 6 and the distance z between the recordingmarks 21 satisfy a relational expression of g=0.5071 z to 3.286 z, thennear-field light is irradiated on the recording mark 21 at a fieldintensity of about 60% of the peak value.

Furthermore, the above mathematic expression 8 is employed to find therange of the gap size g that allows the variable Δ to reach about 90%(Δ=0.9) of the peak value. As a result, it is found that such a gap sizeis in the range of about 0.9284 z to 2.087 z. In other words, if the gapsize g between two conductors 6 and the distance z between the recordingmarks 21 satisfy a relational expression of g=0.9284 z to 2.0787 z, thennear-field light is irradiated on the recording mark 21 at a fieldintensity of about 90% of the peak value.

Specific Examples

The validity of an optimal relationship between the gap size g betweenthe paired conductors 6 and the distance z between the conductor 6 andthe recording mark 21 as described above was evaluated using the FDTDsimulation. Referring now to FIG. 29, the model of the simulationanalysis and the outline of the analytical conditions will be described.FIG. 29 is an enlarged cross-sectional view of the boundary portionbetween the recording medium 20 and the flying slider head (near-fieldlight generating unit 4).

In this simulation analysis, the substrate 5 of the near-field lightgenerating unit 4 is made of SiO₂ and the conductors 6 are made of Au.In addition, recording marks 21 are formed of Co, and a diamond-likecarbon film as a protective film 20 b is formed on the surfaces of therespective recording marks 21. Furthermore, the distance between thesurface of the conductor 6 and the surface of the protective film 20 b(the thickness of an air layer 100) is set to 5 nm and the thickness ofthe protective film 20 b is set to 2 nm. In other words, the distance zbetween the conductor 6 and the recording mark 21 is set to 7 nm. Inaddition, each of the conductors 6 has a length (L) of 220 nm and athickness (t) of 100 nm (see FIG. 2). In this example, furthermore, themid-position between the surfaces of the paired conductors 6 is definedas the origin of coordinates of the X axis, the Y axis (the axis in thedirection perpendicular to the drawing) and the Z axis.

Furthermore, the simulation analysis of this example is not able tocalculate the electric field of the boundary between the recording mark21 and the protective film 20 b because of the specifications of asimulation model used in this analysis. Thus, the field intensity |E|2at a given position (Z=+8 nm), 1 nm inside from the boundary to therecording mark 21, was determined.

In other words, the field intensity |E|2 at a position of (X, Y, Z)=(0,0, +8 nm) was determined.

The results are plotted in FIG. 30.

FIG. 30 illustrates a characteristics chart, where the horizontal axisrepresents the gap size g between the paired conductors 6 and thevertical axis represents the field intensity |E|² at a given position ofZ=+8 nm. As is evident from FIG. 30, the field intensity |Ey|² variesdepending on the gap size g between the paired conductors 6 just as inthe case with FIG. 27. the maximum field intensity can be obtained whenthe gap size g is about 12 nm. On the other hand, the gap size g at themaximum field intensity is calculated by substituting z=8 nm in theabove mathematic equation 1, resulting in g=11.3 nm (dashed line in FIG.30). From these results, it is found that the gap size g obtained at themaximum field intensity obtained by FDTD and the gap size obtained bythe above mathematic expression 1 are well coincident with each other.From this results, it is found that, when the relation of the abovemathematical expression 1 is established during the informationrecording, the maximum field intensity of near-field light irradiated onthe recording mark 21 is attained. Thus, the near-field light can beefficiently irradiated on the recording medium 20.

The above embodiments and the modified examples thereof have beenapplied to the disc-shaped recording media in the above description.However, any of the embodiments of the present invention is not limitedto such disc-shaped recording media. Alternatively, a recording mediumof any shape other than the disc shape, such as a card-shaped recordingmedium, may be used and such a recording medium may exert the sameeffects as those of the disc-shaped recording medium.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2008-324272 filedin the Japan Patent Office on Dec. 19, 2008, the entire content of whichis hereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A recording/reproducing apparatus, comprising: an optical source; anda near-field light generating unit including a substrate transparent tolight from the optical source, two conductors facing each other at apredetermined distance to generate near-field light between said twoconductors by irradiation of the light from said optical source, the twoconductors being formed on the substrate, a top surface of each of thetwo conductors being flush with a top surface of the substrate, the topsurface of each of the two conductors spanning an entire horizontalcross-sectional area of a corresponding conductor, wherein said twoconductors are arranged so that a direction along which said twoconductors face to each other is substantially in parallel with thelongitudinal direction of a recording mark region prepared from apredetermined recording material and having shape anisotropy wheninformation is recorded on a recording medium on which said recordingmark is independently formed.
 2. The recording/reproducing apparatusaccording to claim 1, wherein said two conductors have their respectiveconvex portions facing to each other.
 3. The recording/reproducingapparatus according to claim 1, wherein a side of said recording markregion facing said two conductors is in the shape of a rectangle.
 4. Therecording/reproducing apparatus according to claim 1, wherein a side ofsaid recording mark region facing said two conductors is in the shape ofan ellipsoid.
 5. The recording/reproducing apparatus according to claim1, wherein a center positions of recording marks on tracks adjacent toeach other are staggered in a line direction of said recording medium.6. The recording/reproducing apparatus according to claim 1, wherein apolarization direction of light emitted from said optical source issubstantially in parallel with a direction along which said twoconductors face to each other.
 7. A recording/reproducing apparatus,comprising: an optical source; and a near-field light generating unitincluding a substrate transparent to light from the optical source, twoconductors facing each other at a predetermined distance to generatenear-field light between said two conductors by irradiation of the lightfrom said optical source, the two conductors being formed on thesubstrate, an entire top surface of each of the two conductors beingflush with a top surface of the substrate, wherein said two conductorsare arranged so that a direction along which said two conductors face toeach other is substantially in parallel with the longitudinal directionof a recording mark region prepared from a predetermined recordingmaterial and having shape anisotropy when information is recorded on arecording medium on which said recording mark is independently formed,and a relationship represented by g=2^(1/2)·z is substantiallyestablished, where z is a distance between said conductor and aninformation-recording surface of said recording medium when saidnear-field light is irradiated on said recording medium; and g is apredetermined distance between said two conductors.
 8. A recordreproduction system, comprising: a recording medium on which recordingmark regions having shape anisotropy are independently formed of apredetermined recording material; an optical source; a near-field lightgenerating unit including a substrate transparent to light from theoptical source, and two conductors facing each other at a predetermineddistance to generate near-field light between said two conductors byirradiation of the light from said optical source, wherein the twoconductors are formed on the substrate and a top surface of each of thetwo conductors being flush with a top surface of the substrate, the topsurface of each of the two conductors spanning an entire horizontalcross-sectional area of a corresponding conductor, said two conductorsare arranged so that a direction along which said two conductors face toeach other is substantially in parallel with the longitudinal directionof said recording mark when information is recorded on a recordingmedium using said near-field light.
 9. The recording/reproducingapparatus according to claim 1, wherein the light from the opticalsource irradiates the near-field light generating unit from a bottomsurface of the substrate.
 10. The recording/reproducing apparatusaccording to claim 2, wherein each of the two conductors is formed as atriangle, and the convex portions facing each other are respectivecorners of each triangle.
 11. The recording/reproducing apparatusaccording to claim 10, wherein the two conductors are arranged to form abow-tie pattern.
 12. The record reproduction system according to claim8, wherein the light from the optical source has a wavelength of 780 nm.